1. Field of Invention
The present invention relates to a gate switch apparatus of a LCD, and particularly to a gate switch apparatus of an amorphous silicon LCD (a-Si LCD).
2. Description of the Related Art
A LCD is a display designed according to the liquid crystal principle and liquid crystal mechanism. Normally, liquid crystal can free flow like liquid. However, the molecules in liquid crystal are arranged in a certain pattern, so the optic characteristic thereof is unstable and easily affected by outside conditions, such as electric field, temperature and pressure. The variation of the outside conditions would cause optoelectronic effects with the liquid crystal. LCDs are categorized in two driving modes, a simple-matrix mode and an active-matrix mode, wherein LCDs in active-matrix mode can be a tri-terminal structure such as the typical products of MOSFET-LCD (metal oxide semiconductor field effect transistor LCD) and TFT-LCD (thin film transistor LCD). Among all LCDs in the active-matrix mode, the TFT-LCD has the most potential. In the TFT-LCD field, there are two widely developed technologies, the amorphous silicon TFT (a-Si TFT) and the low-temperature polysilicon TFT (LTPS TFT).
In fact, TFT-LCDs have wide applications, such as calculators, watches, game devices, regular electric appliances, portable electronic dictionaries, word processors, notebook PC, workstations and flat-panel plasma TV.
However, in designing a high-resolution TFT-LCD in the prior art, the number of channels required in the driver thereof is higher, which leads an increased production cost. In addition, an increasing junction points in the driver of a high-resolution TFT-LCD raises the difficulty of assembly in the manufacturing process.
To solve the above-described problems, in a conventional driving system of LTPS TFT, TFTs are used as switches because the electrons move fast enough. The source driver herein is designed as a common source output signal with a switching function, so that each output channel for driving the IC is able to drive a plurality of LCD data lines at different time segment. Thus, the required channel of a source driver is reduced, which accordingly reduces the production cost.
Referring to FIG. 5, a schematic active-matrix circuit drawing of a conventional LTPS LCD is shown, wherein a gate driver 500 is at the left side and a source driver 510 is at the bottom. The gate driver 500 provides an addressing signal, which coordinates with a timing control to turn on or off the TFT gate in sequence and further control the turning on/off of TFTs. Thus, a gray-level data voltage provided by the source driver 510 can charge the storage capacitors such that the gray-level data voltage stored in the storage capacitors are is saved. Further, the gray-level data voltage of the storage capacitor is transferred or read, to become the voltage value of the LCD device. Accordingly, a displaying process of a pixel unit (including a TFT, a storage capacitor and a LCD device) is then completed.
Based on the excellent conductive characteristic of a polysilicon TFT, a LTPS LCD utilizes the common output channels of the source driver 510 for reducing the number of the original source output channels by two thirds; i.e. only one third of the original source output channels remains.
On the other hand, in an a-Si TFT-LCD, since the impedance of an a-Si TFT tends to be very large when an a-Si TFT is on, the TFT width therefore must be widened to reduce the impedance thereof. As a result, the size of the transistor must be increased, and the number of pixel units may be accordingly reduced. For a high-resolution a-Si LCD, such design is seriously flawed. Therefore, the conventional design does not fit to serve as a switch, and further complicates the design and mass production process.